The present invention relates to an inflatable seat belt unit comprising a webbing, which is formed at least partially in bag-like shape, normally maintained in band-like shape, and inflated and developed by a gas generated by gas generating means in an emergency.
Conventionally, a seat belt unit is provided on a seat of a vehicle, such as automobile in most cases, and the seat belt unit restrains an occupant of the vehicle in an emergency such as vehicle collision and protects him or her from injury caused by collision of car body. In such seat belt unit, however, the width of the webbing of the belt restraining the occupant is not very large, and relatively high local load is applied when the occupant is restrained by the webbing.
To solve the problem, inflatable seat belt units have been proposed, for example, in the Japanese Patent Laid-Open Publications No. 47-26830 or No. 49-88220. In such inflatable seat belt unit, a webbing is formed in bag-like shape, and this is maintained in a band-like shape in the normal case, functioning as an ordinary seat belt. In an emergency, the webbing is inflated by introducing gas injected from a gas generating means into the bag-Like webbing and the occupant is received by the inflated webbing, which serves, thus, as an air belt. In this inflatable seat belt unit, the webbing receives kinetic energy of the occupant over wider area. As the result, the load is dispersed, and a high local Load is not applied on the occupant. This provides more effective protection for the occupant.
When an air bag unit is mounted on a rear seal of the vehicle, similarly to the case where it is mounted for the occupant on front seat, the air bag unit must be mounted on a backside of the front seat in front of the rear seat. However, when the air bag unit is mounted on the front seat, it is difficult to protect the occupant on the rear seat properly and effectively because the front seat is adjusted and displaced in front-back direction by the occupant or it is inclined at different position. For this reason, the inflatable seat belt unit as described above is especially effective when it is mounted on rear seat.
In the seat belt unit as disclosed in the above patent publications, a tongue is slidably mounted on the webbing by passing the inflated webbing through a hole of the tongue. When such tongue is used, the webbing does not fit well the occupant when the webbing is twisted or inversed, and smooth movement of the tongue to the webbing may be hindered. Accordingly, the belt through-hole of the tongue must be designed in such size that the webbing is not twisted or inversed. As the result, the size of the: hole is limited.
When the size of the belt through-hole for the tongue is limited, inflation of the webbing is suppressed by the tongue when the gas from the gas generating means is introduced into the bag-like webbing in an emergency and the webbing is inflated. As the result, the introduced gas does not smoothly flow to the portion of the webbing ahead of the tongue, i.e. the portion of the webbing, which contacts the occupant, and this contact portion of the webbing may not be inflated rapidly and perfectly in some cases. In general, the webbing is folded at the belt through-hole. This means that gas flow area is not large enough, and smooth movement of gas is further hindered.
If the contact portion of the webbing is not inflated rapidly and perfectly, the load due to kinetic energy of the occupant is dispersed by the webbing. As the result, the function of the air belt for preventing the application of high local load on the occupant may not be fulfilled reliably and sufficiently.
The tongue is slidably mounted on the inflated webbing, but the inflated webbing is formed in bag-like shape and is hence relatively thick. Thus, it is difficult to move the tongue smoothly, and maneuverability of the tongue is not always satisfactory.